I first became familiar with this when a real life story of people hiding from a patrol during the Korean war was broadcast as part of a documentary in the UK, the mother of the child drowned it in a puddle in order that the group would survive. It was the mother and father who told the story, they both broke down in tears. It was the most heart breaking story of war that I've heard, although Sophies choice and others are probably objectively the same.
I know this. There is no crime that a man will not commit to save himself. I am probably no different. In fact I know that if I was in a group and they needed me to be that guy and carry that sin or trauma that they could all live I may do it. Although I would seek retaliation and it would be as horrifying and bloody as the killing of the baby.
In the past in certain situations which where unsafe or risky or where an aggressor was threatening me and others I've been able to shut of my every day self and act in a way to resolve the situation, conscience does exact a penalty but it does not get in the way at the time, I've investigated Zen, forgiveness as a philosophical and spiritual idea, different theories about mindfulness to offset this kind of thing.
The best depiction I've ever seen of this in literature is actually in the graphic novel "born" which is a kind of genesis of Marvel's The Punisher and depicts Frank Castle's experiences in Vietnam. The skull motif associated with the character is depicted as a kind of inner voice which speaks to Frank, like doing a deal with the devil, telling him that he can "get us out of this" at a point in which Frank's position is being over run, in order to survive Frank concedes to this psychological shadow and goes into a berserker rage. The book finishes with a point that its his family which are the only thing preventing the shadow dominating completely, which I thought made sense as in the Punisher mythos its the murder of his family by mobsters which motivates his Death Wish like punisher campaign of violence.